Species assignment and hybrid identification among Scandinavian hares Lepus europaeus and L. timidus

In Scandinavia, suspected hybrids between the native mountain hare Lepus timidus and the introduced brown hare L. europaeus have been observed by hunters since the first introductions of brown hares in the late 19th century. Several attempts to verify the status of these suspected hybrids have been unsuccessful. Recently, however, the transmission of mitochondrial DNA (mtDNA) from mountain hares to brown hares was documented and interpreted as a consequence of hybridisation and subsequent introgression. However, mtDNA markers alone will not allow identification of first‐generation hybrids because of the strictly maternal inheritance of mitochondria. Here, we combine mtDNA data with analyses of variation in seven microsatellite loci among brown hares, mountain hares and putative hybrids. Our purpose was to determine species differentiation in nuclear DNA markers, elucidate the extent of interspecific gene flow, identify true hybrids within our sample and evaluate the ability of hunters to identify hybrids. The estimated genetic difference between species was low (FST = 0.18 – 0.24, RhoST = 0.09 – 0.16). We believe these low estimates result from a reticulated mode of evolution among hares, with repeated gene flow over the species barrier. Population assignment tests and randomly assembled, artificial, hybrid genotypes were used to classify individuals independently from the morphologically assessed species identity. More than half (57%) of the putative hybrid specimens were assigned unambiguously to either species and first‐generation hybrids seem to be rare. Morphological plasticity and backcrossing, which confound species identification within the genus Lepus, might explain invalid classifications by hunters.